Schottky charge-coupled device infrared sensor arrays are known. The sensor arrays are fabricated in silicon, but only about 20-30% of the area of the silicon crystal is infrared-sensitive. Thus it would give a great increase in sensitivity of the sensor array if incoming light could be focused onto the infrared-sensitive portions of the array. Since the sensor areas are generally longer in one direction than in the other, a cylindrical lens array would greatly increase the sensitivity of the sensor device.
However, the fabrication of such a lens array has many problems. The lens material must be transparent to infrared light, i.e., light of 3-5 micron wavelength; it must be of high quality in terms of lens profile uniformity and smoothness to achieve a uniform focal plane with a minimum of random scattered light; it must be cost effective; and, since the sensor array must operate at very low temperatures, on the order of -196.degree. C., e.g., liquid nitrogen temperatures, it must have an expansion coefficient closely matched to the sensor array material which is silicon. Otherwise the lens array cannot maintain registration with the sensor array at various temperatures. The last requirement practically dictates that the lens array also be made of silicon.
Heretofore lens arrays in silicon have been attempted to be made by cutting, as with a diamond tool. However, since a typical sensor array is an array of 32.times.64 infrared sensor elements and up to 68.times.128 elements, it is obvious that the lens array periodicity must be accurate to within .+-.0.1% across the silicon chip to maintain accurate registration between the individual lenses and the individual sensors or detectors. Thus the problems of manufacture are far from trivial.